The outcrop rocks investigated by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum consist of altered basaltic fines emplaced through aeolian and aqueous processes. Diagenesis through episodes of groundwater influx is likely responsible for lithification of the sediments, formation and subsequent dissolution of embedded crystals, and development of hematitic spherules with occasional cemented overgrowths . The action of liquid water in the development of these rocks prompts the search for pure evaporative salts such as chlorides. Extensive deposits of this nature have not yet been discovered and may be a result of erosion and removal from stratigraphic layers above those sampled by Opportunity, or burial beneath accessible depths . Nonetheless, the presence of small amounts of halite (NaCl) associated with coatings and rinds is indicated by the available data.